Porous titania, catalyst comprising the porous titania

ABSTRACT

The present invention provides a porous titania, which has an anatase-form crystalline structure, an anatase-form crystallite diameter of 3 nm to 10 nm, a degree of anatase crystallinity of 60% or more, a BET specific surface area of 10 m 2 /g or more, a total pore volume of 0.05 cm 3 /g or more, and a volume for pores having a pore radius of 1 nm or more of 0.02 cm 3 /g or more, and the porous titania and the catalyst comprising the porous titania of the present invention exhibit an excellent catalytic activity for removal of nitrogen oxides, oxidation of organic substances, decomposition of dioxine compounds, as well as decomposition and removal of organic solvents, agricultural chemical and surfactant.

This is a continuation application of U.S. application Ser. No.09/635,078, filed Aug. 9, 2000.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to a porous titania, a catalyst comprisingthe porous titania, a method for producing the porous titania and amethod for the catalyst comprising the porous titania. Specifically, thepresent invention relates to a porous titania which can be used as acatalyst, and a catalyst comprising the porous titania, which can beused for removal of nitrogen oxides, oxidation of organic substances,decomposition of dioxine compounds, or decomposition and removal oforganic solvents, surfactant and the like.

2. Description of the Related Art

Titania catalysts are known as catalysts for removal of nitrogen oxidesin order to remove nitrogen oxides contained in waste gases fromincinerators. Various improvements have previously been proposed fortitania catalysts in order to attain long term retaining of catalystactivity. For example, JP-A-5-184923 discloses that a titania catalystcan be obtained by heat-treating amorphous fibers to deposit a crystalof an anatase-form titanium oxide and a vanadium oxide, in whichamorphous fibers is produced by the sol-gel method of hydrolyzing aalkoxide in a mixed solution of a titanium alkoxide, a vanadium compoundand other alkoxide, successively gelling.

The titania catalyst described in JP-A-5-184923, however, has problemsin that the activity is low and the performance of removal of nitrogenoxides is low.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a porous titania whichcan be used as a catalyst for removal of nitrogen oxides, oxidation oforganic substances, decomposition of dioxine compounds, or decompositionand removal of organic solvents, surfactant and the like.

An other object of the present invention is to provide a catalystcomprising the porous titania, which can be used for removal of nitrogenoxides, oxidation of organic substances, decomposition of dioxinecompounds, or decomposition and removal of organic solvents, surfactantand the like.

An other object of the present invention is to provide a method forproducing the porous titania.

An other object of the present invention is to provide a method forproducing the catalyst comprising the porous titania.

The present inventors have devoted intensive efforts to improvingcatalytic activity of titania. As a result, the present inventors havediscovered a porous titania having a high degree of anatasecrystallinity, a large specific surface area and a large pore volume,which is obtainable by adding a mixed solution containing water and asolvent to the titanium alkoxide solution to perform hydrolysis andsimultaneous polymerization to give a polymer solution, adding a fattyacid to the titanium alkoxide solution or the polymer solution,separating a polymer containing the fatty acid from the polymersolution, and calcining the polymer containing the fatty acid, whichexhibits an excellent catalytic activity for removal of nitrogen oxidesand the like.

Therefore, the present invention provides a porous titania, which has ananatase-form crystalline structure, an average crystallite diameter of 3nm to 10 nm, a degree of anatase crystallinity of 60% or more, a BETspecific surface area of 10 m²/g or more, a total pore volume of 0.05cm³/g or more, and a volume of pores having a pore radius of 1 nm ormore of 0.02 cm^(3/)g or more.

The present invention also provides a catalyst formed by molding theporous titania described above.

The present invention also provides a catalyst comprising the poroustitania described above and at least one catalyst component selectedfrom the group consisting of V, W, Al, As, Ni, Zr, Mo, Ru, Mg, Ca, Fe,Cr and Pt.

The present invention also provides a method for producing the poroustitania described above, which comprises the steps of:

dissolving a titanium alkoxide in a solvent to give a titanium alkoxidesolution;

adding a mixed solution containing water and a solvent to the titaniumalkoxide solution to perform hydrolysis and simultaneous polymerizationto give a polymer solution;

adding a fatty acid to the titanium alkoxide solution or the polymersolution;

separating a polymer containing the fatty acid from the polymersolution; and

calcining the polymer containing the fatty acid.

The present invention also provides a method for producing the catalystdescribed above, which comprises the steps of:

dissolving a titanium alkoxide in a solvent to give a titanium alkoxidesolution;

adding a mixed solution containing water and a solvent to the titaniumalkoxide solution to perform hydrolysis and simultaneous polymerizationto give a polymer solution;

adding a fatty acid to the titanium alkoxide solution or the polymersolution;

adding at least one catalyst component selected from the groupconsisting of V, W, Al, As, Ni, Zr, Mo , Ru, Mg, Ca, Fe, Cr and Pt tothe titanium alkoxide solution or the polymer solution;

separating a polymer containing the fatty acid and the catalystcomponent from the polymer solution; and

calcining the polymer containing the fatty acid and the catalystcomponent.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

DETAILED DESCRIPTION OF THE INVENTION

Titania has a chemical formula: TiO₂ and is known to have a crystallinestructure of anatase-form, rutile-form or amorphous structure. Theporous titania of the present invention has an anatase-form crystallinestructure and has here a requirement that its crystallite diameter isabout 3 nm or more and about 10 nm or less as calculated by theScherrer's equation based on a half width of peak and a peak position in(101) plane of anatase obtained by X-ray diffraction method. It ispreferred that the crystallite diameter is about 5 nm or more and about9 nm or less.

The second requirement for identifying the porous titania of theinvention is a degree of anatase crystallinity. The degree of anatasecrystallinity can be calculated by measuring a peak area of (101) planeof anatase by X-ray diffraction method. In the present invention, it isrequired that the degree of anatase crystallinity is about 60% or more.It is preferred that the degree of anatase crystallinity is about 65% ormore, further about 70% or more, and about 95% or less, further about90% or less. It is difficult to obtain a sufficient activity as acatalyst when the porous titania has the degree of anatase crystallinityof less than about 60%, even if the anatase crystallite diameter asdescribed above falls within a range of about 3 nm to about 10 nm.

Other requirements for identifying the porous titania of the inventionis a BET specific surface area, a total pore volume and a volume forpores having a pore radius of about 1 nm or more. In the presentinvention, it is required that the BET specific surface area is about 10m²/g or more, the total pore volume is about 0.05 cm³/g or more, and thevolume for pores having a pore radius of about 1 nm or more is about0.02 cm³/g or more. It is preferred that the BET specific surface areais about 180 m²/g or more, further about 200 cm²/g or more, the totalpore volume is about 0.2 cm³/g or more, and the volume for pores havinga pore radius of about 1 nm or more is about 0.2 cm³/g or more. It isdifficult to obtain a porous titania having an excellent catalyticactivity when the BET specific surface area is less than about 10 m²/g,the total pore volume is less than about 0.05 cm³/g, or the volume forpores having a pore radius of about 1 nm or more is less than about 0.02cm³/g. The BET specific surface area, the total pore volume, and thevolume for pores having a pore radius of about 1 nm or more can bemeasured by continuous volume method using nitrogen gas.

In addition to fact that the porous titania of the invention meets therequirements relating to the anatase crystallite diameter, the degree ofanatase crystallinity, the BET specific surface area, the total porevolume, and the volume for pores having a pore radius of about 1 nm ormore, it is preferred that it has a pore structure exhibiting a maximumin a range of a pore radius of about 1 nm or more and about 30 nm orless, preferably about 1 nm or more and about 10 nm or less, in adistribution curve of pore volumes plotted against pore radii.Particularly, when the porous titania of the present invention has afibrous shape, the fibrous porous titania having a pore structuredescribed above is excellent in the catalytic activity and has asufficient tensile strength. The fibrous porous titania has usually atensile strength of about 0.1 GPa or more and an average diameter offibers of about 2 μm to about 50 μm.

The catalyst of the present invention comprises the porous titania ofthe present invention and known catalyst components for removal ofnitrogen oxides or others. The catalyst components include elements suchas V, W, Al, As, Ni, Zr, Mo, Ru, Mg, Ca, Fe, Cr, Pt and the like.

By molding the porous titania and the catalyst of the present inventioninto various shapes such as sphere, ring, honeycomb, fiber or sheet byusing a known method, the porous titania and the catalyst of theinvention are usually used for removal of nitrogen oxides, and inaddition, for oxidation of organic substances, decomposition of dioxinecompounds or decomposition and removal of organic solvents, agriculturalchemicals or surfactants in water.

The porous titania of the present invention can be obtained, forexample, by a method comprising: dissolving a titanium alkoxide in asolvent to give a titanium alkoxide solution; adding a mixed solutioncontaining water and a solvent to the titanium alkoxide solution toperform hydrolysis and simultaneous polymerization to give a polymersolution; adding a fatty acid to the titanium alkoxide solution or thepolymer solution; separating a polymer containing the fatty acid fromthe polymer solution; and calcining the polymer containing the fattyacid.

The titanium alkoxide used in the production of the porous titania ofthe invention includes titanium alkoxides represented by the followingformula (I):

Ti(OR₁)₄  (I)

wherein R₁ represents an alkyl group having 1 to 4 carbon atoms.Examples include titanium tetramethoxide, titanium tetra-ethoxide,titanium tetra-n-propoxide, titanium tetra-isopropoxide, titaniumtetra-n-butoxide, titanium tetra-sec-butoxide, titaniumtetra-tert-butoxide. Amongst them, application of titaniumtetra-isopropoxide is preferred. When R₁ in the formula (I) is an alkylgroup having 5 or more carbon atoms, the mechanical strength of theobtained porous titania may be low.

For the solvent used, any solvent capable of dissolving a titaniumalkoxide can be applied. Examples include alcohols, ethers and aromatichydrocarbons. The alcohols include compounds represented by thefollowing formula (II):

R₂OH  (II)

wherein R₂ represents an alkyl group having 1 to 4 carbon atoms.

Examples include ethanol, isopropyl alcohol and the like. The ethersinclude tetrahydrofuran, diethyl ether and the like. It is preferredthat the solvent used for dissolving the titanium alkoxide is of thesame kind as the solvent used for preparation of the mixed solutioncontaining water and the solvent to be added for hydrolysis purpose. Theamount of the solvent used for dissolving the titanium alkoxide isusually within a range of about 0.5 to about 50 moles based on 1 mole oftitanium alkoxide.

The fatty acid to be used includes compounds represented by thefollowing formula (III):

R₃COOH  (III)

wherein R₃ represents hydrogen or a saturated or unsaturated hydrocarbonresidue.

Examples of the saturated fatty acid include formic acid, acetic acid,propionic acid, butyric acid, isobutyric acid, valeric acid, caproicacid, enanthylic acid, caprylic acid, pelargonic acid, capric acid,undecylic acid, lauric acid, tridecylic acid, myristic acid,pentadecylic acid, palmitic acid, heptadecylic acid, isostearic acid,nonadecanic acid, arachic acid, behenic acid, lignoceric acid, ceroticacid, heptacosanic acid, montanic acid, melissic acid, lacceric acid andthe like. Examples of unsaturated fatty acid include acrylic acid,crotonic acid, isocrotonic acid, undecylenic acid, oleic acid, elaidicacid, cetoleic acid, erucic acid, brassidic acid, sorbic acid, linolicacid, linoleic acid, arachidonic acid, propiolic acid, stearolic acidand the like. Amongst them, application of fatty acids represented bythe formula (III) wherein R₃ is a saturated or unsaturated hydrocarbonresidue having about 8 or more carbon atoms is preferred. The amount ofthe fatty acid in the polymer solution depends on the kind thereof andis not critical. Usually, it is about 0.01 mole or more, preferablyabout 0. 05 mole or more and about 0.5 mole or less, preferably about0.3 mole or less based on 1 mole of titanium alkoxide used for thepreparation of the polymer solution. When the amount of fatty acid isless than about 0.01 mole, a porous titania having an excellentcatalytic activity may not be obtained. When the amount of fatty acid isgreater than about 0.5 mole, the mechanical strength of the poroustitania obtained may be low.

The fatty acid may exist by any means in which it is in thepredetermined amount in the polymer solution, and may be present, forexample, by a method in which the fatty acid is added to the titaniumalkoxide solution or a method in which the fatty acid is added to thepolymer solution.

In a method for producing the catalyst of the present invention, acompound or the like containing at least one element selected from thegroup consisting of V, W, Al, As, Ni, Zr, Mo, Ru, Mg, Ca, Fe, Cr and Ptas catalyst components is added to the titanium alkoxide solution or amethod in which the fatty acid is added to the polymer solution asaddition of the fatty acid.

The compound includes vanadium compounds such as vanadium alkoxides,vanadyl alkoxides, triethoxy vanadyl, vanadium acatylacetonate, vanadiumchloride and vanadyl chloride; tungsten compounds such as tungstenalkoxides and tungsten chloride; aluminum compounds such as aluminumalkoxides and aluminium chloride; arsenic compounds such as arsenicchloride; nickel compounds such as nickel alkoxide and nickel chloride;zirconium compounds such as zirconium alkoxides, zirconiumacetylacetonate, zirconium butoxyacetylacetonate and zirconiumtetrabutoxide; molybdenum compounds such as molybdenumoxyacetylacetonate and molybdenum chloride; ruthenium compounds such asruthenium chloride; magnesium compounds such as magnesium alkoxides,magnesium acetylacetonate and magnesium chloride; calcium compounds suchas calcium alkoxides and calcium chloride; iron compounds such as ironalkoxides, iron acetylacetonate and iron chloride; chromium compoundssuch as chromium alkoxides and chromium acetylacetonate; platinumcompounds such as platinum acetylacetonate and platinum chloride; and soon. Amongst them, vanadium alkoxides is a generic name includingvanadium methoxide, vanadium ethoxide, vanadium n-propoxide, vanadiumisopropoxide, vanadium n-butoxide, vanadium sec-butoxide, vanadiumtert-butoxide and the like.

The porous titania having a fibrous shape is described below in detail.The fibrous porous titania can be obtained by a method, which comprisesthe steps of:

dissolving a titanium alkoxide in a solvent to give a titanium alkoxidesolution and adding a mixed solution containing water and a solvent to atitanium alkoxide solution to perform hydrolysis and simultaneouspolymerization to give a polymer solution (hereinafter, referred to asstep (1));

dissolving the polymer in an organic solvent in which the polymer issoluble to give a spinning solution (hereinafter, referred to as step(2));

spinning the spinning solution to give a precursor fiber (hereinafter,referred to as step (3)); and

calcining the precursor fiber (hereinafter, referred to as step (4)).

In this method, a polymer is separated from the polymer solution as aprecursor fiber.

The step (1) can be conducted by a method in which a mixed solution ofwater and a solvent is added to a titanium alkoxide solution obtained bydissolving a titanium alkoxide of the above-described formula (I) in asolvent to hydrolyze titanium alkoxide and simultaneously polymerize. Asthe solvent used for dissolving the titanium alkoxide and the solventused for preparing the mixed solution to be added for hydrolysis,various solvents in which titanium alkoxide is soluble can be applied.Examples include alcohols, ethers and aromatic hydrocarbons. Thealcohols are represented by the above-described formula (II). The mixedsolution has a water content of about 1% by weight to about 50% byweight. The amount to be added is usually within a range of about 1.5mole to about 4 moles converted to H₂O based on 1 mole of titaniumalkoxide used as the raw material.

In the step (1) it is preferred that a mixed solution of water and asolvent is added to a titanium alkoxide solution obtained by dissolvinga titanium alkoxide in a solvent to hydrolyze titanium alkoxide andsimultaneously polymerize in an inert gas atmosphere such as nitrogen.When a fatty acid represented by the above-described formula (III) isadded, the method can be carried out by a method in which a fatty acidin the predetermined amount is added to the titanium alkoxide solution.In this case, when the amount of fatty acid is greater than about 0.5mole, it becomes difficult to obtain a fibrous porous titania having asufficient tensile strength. It is also possible to add the fatty acidto the polymer solution or the spinning solution.

When catalyst components described above is added, the amount of thecatalyst component to be added depends on its use. For example, for theapplication of removal of nitrogen oxides, the amount converted to oxideis about 0.001% by weight to about 50% by weight based on the obtainedtitania catalyst. It is also possible to add the catalyst component tothe titanium alkoxide solution, the polymer solution or the spinningsolution.

In case where a polymer formed in the titanium alkoxide solutionprecipitates in the step (1), the concentration of the spinning solutioncan be adjusted after removal of the solvent or partial removal of thesolvent. On the other hand, in case where a polymer formed in thetitanium alkoxide solution does not precipitate, the concentration ofthe spinning solution can be adjusted directly.

In the hydrolysis and polymerization of the titanium alkoxide solutionin the step (1), it is preferred, concurrently with addition of a mixedsolution of water and a solvent, to reflux the titanium alkoxidesolution and to distil out the same amount of the solvent as the solventcontained in the mixed solution under addition. By conducting thehydrolysis and polymerization in such manner, lowering of concentrationof titanium in the titanium alkoxide solution after the hydrolysis andpolymerization can be prevented.

The step (2) can be conducted by a method in which a polymer obtained inthe step (1) is dissolved in an organic solvent in which the polymer issoluble in an inert gas atmosphere such as nitrogen gas. For the organicsolvent, any solvent capable of dissolving a fatty acid used in theproduction of the porous titania can be applied. Examples includealcohols such as ethanol, isopropyl alcohol, ethers such astetrahydrofuran, diethyl ether and aromatic hydrocarbons such asbenzene, toluene.

In the step (2), it is preferred that the polymer obtained in the step(1) is dissolved in an organic solvent to give a polymer solution andthen the polymer solution is concentrated by heating or reducingpressure so that a spinning solution having a polymer concentration ofabout 50% by weight to about 80% by weight is prepared. The viscosity ofthe obtained spinning solution at 40° C. is usually about 10 poise (1Pa·s) to about 2,000 poise (200 Pa·s) and preferably about 20 poise (2Pa·s) to about 1,500 poise (150 Pa·s).

The step (3) can be conducted by a method in which a spinning solutionobtained in the step (2) is subjected to any kind of spinning such asnozzle-extruding spinning, centrifugal spinning and blow-out spinning.The obtained precursor fiber can be stretched by rotating rolls or ahigh speed air stream.

The step (4) can be conducted by a method in which a precursor fiberobtained in the step (3), which is contained the fatty acid and thecatalyst component, is calcined at about 200 to about 900° C.

It is preferred that the precursor fiber is subjected to steam treatmentduring, before or after the calcination. The steam treatment may beeffected with a thermo-hygrostate or a calciner. Usually, for steamtreatment, the temperature is about 70° C. or above, preferably about85° C. or above, and about 300° C. or below; the partial pressure ofsteam is about 0.3 atmosphere (0.03 MPa) or above and preferably about0.5 atmosphere (0.05 MPa) or above; and the contacting period is about30 minutes or longer, preferably about 1 hour or longer and morepreferably about 5 hours or longer. When the steam treatment isconducted during the calcination, the treatment may be carried out withadjustment of heating rate while keeping the predetermined humidity by amethod in which steam is blown into a calciner or a method in whichwater is sprayed. In this case, the precursor fiber is hold in anatmosphere having a high partial pressure of steam of about 0.3atmosphere (0.03 MPa) or above between a temperature of about 70 toabout 300° C. for at least about 30 minutes and thereafter may becalcined in an atmosphere having a lower partial pressure of steam.

In the production of the porous titania of the present invention, acompound having an active hydrogen element may be added to the titaniumalkoxide solution. In addition, a silicon compound may be added to thetitanium alkoxide solution or the spinning solution. Preferred compoundhaving an active hydrogen element includes a salicylic acid alkyl ester,or β-diketone compound represented by the following formula (IV):

R₄COCH₂COR₅  (IV)

wherein R₄ represents an alkyl group or an alkoxy group having 1 to 4carbon atoms, and R₅ represents an alkyl group or an alkoxy group having1 to 4 carbon atoms.

Preferred salicylic acid alkyl ester includes ethyl salicylate andmethyl salicylate. Preferred β-diketone compound includes ethylacetoacetate and isopropyl acetoacetate.

The amount of the compound having an active hydrogen element to be addedis about 0.05 mole or more, preferably about 0.1 mole or more and about1.9 mole or less, preferably about 1.0 mole or less, based on 1 mole oftitanium alkoxide.

Preferred silicon compound includes alkyl silicate represented by thefollowing formula (V):

Si_(n)O_(n−1)(OR₆)_(2n+2)  (V)

wherein R₆ represents analkyl group having 1 to 4 carbon atoms, and nrepresents a number of 1 or more. Amongst them, a compound of theformula (V) wherein R₆ is ethyl and n is 4 to 6 is preferable.

The porous titania of the present invention exhibits an excellentcatalytic activity for removal of nitrogen oxides, by using it as acatalyst, the removal of nitrogen oxides can be performed effectively.In addition, when the catalyst of the present invention is applied,removal of nitrogen oxides, oxidation of organic substances,decomposition of dioxine compounds, as well as decomposition and removalof organic solvents, agricultural chemical and surfactant can beperformed effectively. Furthermore, using the porous titania or thecatalyst of the invention, the space required for placing the catalystcan be diminished and the apparatus for waste gas treatment such as theapparatus for removal of nitrogen oxides can be small-sized.

By the method for the production according to the present invention, theporous titania described above can be easily manufactured.

EXAMPLES

The present invention will now be described with reference to Examples,which should not be construed as a limitation upon the scope of theinvention.

In the invention, the anatase-form crystallite diameter, the degree ofanatase crystallinity, the BET specific surface area and pore volumewere measured by methods described below. In Examples, the poroustitania having fibrous shape are used.

(1) Anatase-form Crystallite Diameter

A porous titania was pulverized in a mortar and measured X-raydiffraction spectra by using an X-ray diffraction apparatus (ModelRAD-IIA, manufactured by Rigaku Denki Co.,Ltd.). The crystallitediameter L (nm) was calculated by the following equation using theobtained half width β (radian) of a peak of (101) plane and a peakposition θ (radian).

L=K·λ/(β·cosθ)

wherein K represents the Scherrer's constant: 0.94, and λ (nm)represents a wavelength of X-ray used for measurement (CuKα -ray:0.15406 nm).

(2) Degree of Anatase Crystallinity

A porous titania was pulverized in a mortar and measured X-raydiffraction spectra by using an X-ray diffraction apparatus(ModelRAD-IIA, manufactured by Rigaku Denki Co.,Ltd.). The degree of anatasecrystallinity A (%) was calculated by the following equation using theobtained peak area S₁ of (101) plane.

A=S ₁/(S ₂ ·X)×100

wherein S₂ represents a peak area of (101) plane of the standardsample(trade name: STT-65C-S, manufactured by Titan Kogyo KabushikiKaisha), and X represents a molar fraction of titanium based on thetotal elements except oxygen in the porous titania.

(3) BET Specific Surface Area (m²/g), Total Pore Volume (cm³/g) andVolume for Pores Having a Pore Radius of 1 nm or More (cm³/g)

These values were obtained by continuous volume method using a nitrogengas. That is, these values were calculated from a distribution curve ofvolumes against pore radii which was obtained by using a gas-absorption/desorption analyzer(trade mark: Omunisorp 360, manufactured by CoulterCo., Ltd). In this method, a porous titania was degassed underconditions including a temperature of 130° C., a retention time of 6hours and a vacuum of 6×10⁻⁵ Torr (8 MPa) after pulverizing in a mortar.

(4) Removal Test of Nitrogen Oxides

The 0.2 g of the porous titania was packed in a glass reaction cylinderhaving a inside diameter of 12 mm φ so that a packing height becomes 5mm, and a gas prepared by mixing NO gas, NH₃ gas, air, N₂ and H₂O, whichcontains NO of about 100 ppm, NH₃ of about 100 ppm, O₂ of about 10% andH₂O of about 20% and has a temperature of 200° C., was passed through ata flow rate of 1 NL/min. The inlet NO_(x) concentration and the outletNO_(x) concentration of the reaction cylinder were measured by anautomatic NO_(x) measuring apparatus( model ECL-77A, manufactured byYanagimoto Seisakusyo) and the nitrogen oxides removal efficiency (%)was calculated by the following equation:

Nitrogen oxides removal efficiency (%)={[(inlet NO_(x)concentration)−(outlet NO_(x) concentration)]/(inlet NO_(x)concentration)}×100

Example 1

Into 77.8 g of isopropyl alcohol (extra pure grade reagent, manufacturedby Wako Pure Chemical Industries) as a solvent were dissolved 225 g oftitanium tetra-isopropoxide (1st grade reagent, manufactured by WakoPure Chemical Industries) as a titanium alkoxide, 61.9 g of vanadiumisopropoxide ( manufactured by Nichia Chemical Industries) as a catalystcomponent and 10.3 g of ethyl acetoacetate (extra pure grade reagent,manufactured by Wako Pure Chemical Industries). The mixture was refluxedfor 1 hour in a nitrogen atmosphere to give a titanium alkoxidesolution.

The amount of the catalyst component added here was 27% by weightconverted to vanadium oxide (V₂O₅) based on a fibrous porous titania tobe obtained. The amount of ethyl acetoacetate added was 0.1 mole basedon 1 mole of titanium tetra-isopropoxide.

Then, 32.7 g of water and 294.9 g of isopropyl alcohol were mixed toform a mixed solution having a water concentration of 10% by weight. Theamount of water was 2.30 moles based on 1 mole of titaniumtetra-isopropoxide.

The titanium alkoxide solution obtained above was refluxed in a nitrogenatmosphere, and simultaneously, while distilling out the solvent, themixed solution obtained above was added with stirring. The rate ofdistilling out the solvent was adjusted so that it was almost equal tothe rate of feeding of the solvent due to the addition of the mixedsolution. The period for addition of the mixed solution was 96 minutes.

When the amount of added water was 1.80 mole per 1 mole of titaniumtetra-isopropoxide, precipitation of a polymer began in the titaniumalkoxide solution. When the total amount of the mixed solution wasadded, the titanium alkoxide solution became a polymer slurry.

The obtained polymer slurry was refluxed for 1 hour in a nitrogenatmosphere. Then the solvent was distilled out by heating so that thesolution was concentrated until the titanium concentration in thepolymer slurry was 2.97×10³ mol/g converted to Ti.

To the concentrated polymer slurry was added 273 g of tetrahydrofuran(extra pure grade reagent, manufactured by Wako Pure ChemicalIndustries) as an organic solvent in a nitrogen atmosphere. The mixturewas refluxed for 1 hour to dissolve the polymer.

To the mixture was added 33.8 g of isostearic acid reagent, manufacturedby Wako Pure Chemical Industries) as a fatty acid. The mixture wasrefluxed for 1 hour to give a polymer solution.

The obtained polymer solution was filtered through a membrane filter offluorine-contained resin having a pore diameter of 3 μm in a nitrogenatmosphere and heated in order to distil out the mixed solventconsisting of isopropyl alcohol and tetrahydrofuran to give 247 g of aspinning solution. The spinning solution had a viscosity of 50 poise (5Pa·s) at 40° C.

The spinning solution obtained above was kept at 40° C. and extrudedinto an air atmosphere having a relative humidity of 60% at 40° C. froma nozzle having a hole diameter of 50 μm using 20 kg/cm2 (2 MPa)nitrogen gas. The product was taken up at a rate of 70 m/min to giveprecursor fibers.

The obtained precursor fibers were treated with steam in athermo-hygrostat controlled at a temperature of 85° C. and a relativehumidity of 95% for 15 hours. Then they were heated .at a rate of 200°C./hour and calcined in the air at 350° C. for 1 hour to give a fibrousporous titania having an anatase-form crystalline structure and a fiberdiameter of 15 μm.

Physical properties of the obtained a fibrous porous titania and thenitrogen oxides removal efficiency obtained in the test are shown inTable 1.

Example 2

The procedure in Example 1 was repeated except that the calcinationtemperature was changed from 350° C. to 400° C. to give a fibrous poroustitania.

Physical properties of the obtained fibrous porous titania and thenitrogen oxides removal efficiency obtained in the test are shown inTable 1.

Example 3

The procedure in Example 1 was repeated except that the calcinationtemperature was changed from 350° C. to 300° C. to give a fibrous poroustitania.

Physical properties of the obtained fibrous porous titania and thenitrogen oxides removal efficiency obtained in the test are shown inTable 1.

Example 4

Into 67.5 g of isopropyl alcohol(extra pure grade reagent, manufacturedby Wako Pure Chemical Industries) as a solvent were dissolved 225 g oftitanium tetra-isopropoxide (1st pure grade reagent, manufactured byWako Pure Chemical Industries) as a titanium alkoxide, 61.9 g ofvanadium isopropoxide (manufactured by Nichia Chemical Industries) as acatalyst component and 20.6 g of ethyl acetoacetate (extra pure gradereagent, manufactured by Wako Pure Chemical Industries). The mixture wasrefluxed for 1 hour in a nitrogen atmosphere to give a titanium alkoxidesolution.

The amount of the catalyst component added here was 27% by weightconverted to vanadium oxide (V₂O₅) based on a fibrous porous titania tobe obtained. The amount of ethyl acetoacetate added was 0.2 mole basedon 1 mole of titanium tetra-isopropoxide.

Then, 35.5 g of water and 320.5 g of isopropyl alcohol were mixed toform a mixed solution having a water concentration of 10% by weight.

The titanium alkoxide solution obtained above was refluxed in a nitrogenatmosphere, and simultaneously, while distilling out the solvent, themixed solution obtained above was added with stirring. The rate ofdistilling out the solvent was adjusted so that it was almost equal tothe rate of feeding of the solvent due to the addition of the mixedsolution. The period for addition of the mixed solution was 101 minutes.

When the amount of added water was 2.07 mole per 1 mole of titaniumtetra-isopropoxide, precipitation of a polymer began in the titaniumalkoxide solution. When the total amount of the mixed solution wasadded, the titanium alkoxide solution became a polymer slurry.

The obtained polymer slurry was refluxed for 1 hour in a nitrogenatmosphere. Then the solvent was distilled out by heating so that thesolution was concentrated until the titanium concentration in thepolymer slurry was 2.85×10³ mol/g converted to Ti.

To the concentrated polymer slurry was added 269 g of tetrahydrofuran(extra pure grade reagent, manufactured by Wako Pure ChemicalIndustries) as an organic solvent in a nitrogen atmosphere. The mixturewas refluxed for 1 hour to dissolve the polymer.

To the mixture was added a solution of 23.8 g of lauric acid ( reagent,manufactured by Wako Pure Chemical Industries) as a fatty acid dissolvedin 23.8 g of tetrahydrofuran (extra pure grade reagent, manufactured byWako Pure Chemical Industries). The mixture was refluxed for 1 hour togive a polymer solution.

The obtained polymer solution was filtered through a membrane filter offluorine-contained resin having a pore diameter of 3 μm in a nitrogenatmosphere and heated in order to distil out the mixed solventconsisting of isopropyl alcohol and tetrahydrofuran to give 249 g of aspinning solution. The spinning solution had a viscosity of 50 poise (5Pa·s) at 40° C.

The obtained spinning solution was kept at 40° C. and extruded into anair atmosphere having a relative humidity of 60% at 40° C. from a nozzlehaving a hole diameter of 50 μm using 20 kg/cm² (2 MPa) nitrogen gas togive precursor fibers.

The obtained precursor fibers were treated with steam in athermo-hygrostat controlled at a temperature of 85° C. and a relativehumidity of 95% for 15 hours. Then they were heated at a rate of 200°C./hour and calcined in the air at 350° C. for 1 hour to give a fibrousporous titania having an anatase-form crystalline structure and a fiberdiameter of 15 μm.

Physical properties of the obtained fibrous porous titania and thenitorogen oxides removal efficiency obtained in the test are shown inTable 1.

Comparative Example 1

Into 18.1 g of isopropyl alcohol (extra pure grade reagent, manufacturedby Wako Pure Chemical Industries) as a solvent were dissolved 225 g oftitanium tetra-isopropoxide (1st pure grade reagent, manufactured byWako Pure Chemical Industries) as a titanium alkoxide, 61.9 g ofvanadium isopropoxide (manufactured by Nichia Chemical Industries) as acatalyst component and 41.2 g of ethyl acetoacetate (extra pure gradereagent, manufactured by Wako Pure Chemical Industries). The mixture wasrefluxed for 1 hour in a nitrogen atmosphere to give a titanium alkoxidesolution.

The amount of the catalyst component added here was 27% by weightconverted to vanadium oxide (V₂O₅) based on a fibrous porous titania tobe obtained. The amount of ethyl acetoacetate added was 0.4 mole basedon 1 mole of titanium tetra-isopropoxide. Then, 30.6 g of water and275.8 g of isopropyl alcohol were mixed to form a mixed solution havinga water concentration of 10% by weight.

The titanium alkoxide solution obtained above was refluxed in a nitrogenatmosphere, and simultaneously, while distilling out the solvent, themixed solution obtained above was added with stirring. Then the obtainedproduct was refluxed for 1 hour in a nitrogen atmosphere. The solventwas distilled out by heating so that the solution was concentrated untilthe titanium concentration in the polymer slurry was 3.27×10³ mol/gconverted to Ti.

To the concentrated polymer slurry was added 271 g of tetrahydrofuran(extra pure grade reagent, manufactured by Wako Pure ChemicalIndustries) as an organic solvent in a nitrogen atmosphere. The mixturewas refluxed for 1 hour to dissolve the polymer. The mixture wasrefluxed for 1 hour to give a polymer solution.

The obtained polymer solution was filtered through a fluorine-containedresin membrane filter having a pore diameter of 3 μm in a nitrogenatmosphere and heated in order to distil out the mixed solventconsisting of isopropyl alcohol and tetrahydrofuran to give 197 g of aspinning solution. The spinning solution had a viscosity of 50 poise (5Pa·s) at 40° C.

The obtained spinning solution was kept at 40° C. and extruded into anair atmosphere having a relative humidity of 60% at 40° C. From a nozzlehaving a hole diameter of 50 μm using 20 kg/cm² (2 MPa) nitrogen gas togive precursor fibers.

The obtained precursor fibers were treated with steam in athermo-hygrostat controlled at a temperature of 85° C. and a relativehumidity of 95% for 15 hours. Then they were heated at a rate of 200°C./hour and calcined in the air at 400° C. for 1 hour to give a fibrousporous titania having an anatase-form crystalline structure and a fiberdiameter of 15 μm.

Physical properties of the obtained fibrous porous titania and thenitrogen oxides removal efficiency obtained in the test are shown inTable 1.

Comparative Example 2

The procedure in Comparative Example 1 was repeated except that thecalcination temperature was changed from 400° C. to 300° C. to give afibrous porous titania.

Physical properties of the obtained fibrous porous titania and thenitrogen oxides removal efficiency obtained in the test are shown inTable 1.

TABLE 1 Physical properties of porous titania Volume NitogenAnatase-form Degree of Total for pores having oxides crystallite anataseBET surface pore a pore radius removal diameter crystallinity surfacearea volume of 1 nm or more efficiency nm % m²/g cm³/g cm³/g % Ex. 1 6.878 237 0.28 0.28 81 Ex. 2 6.5 87 181 0.24 0.24 75 Ex. 3 6.3 66 282 0.290.29 74 Ex. 4 6.3 71 221 0.20 0.20 70 Comp. 6.6 53 186 0.13 0.13 60 Ex.1 Comp. 5.8 52 232 0.22 0.08 62 Ex. 2

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the sprit and scope of the invention, and suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A porous titania, which has an anatase-formcrystalline structure, an anatase-form crystallite diameter of 3 nm to10 nm, a degree of anatase crystallinity of 60% or more, a BET specificsurface area of 10 m²/g or more, a total pore volume of 0.05 cm³/g ormore, and a volume for pores having a pore radius of 1 nm or more of0.02 cm³/g or more.
 2. A porous titania according to claim 1, whereinthe BET specific surface area is 180 m²/g or more.
 3. A porous titaniaaccording to claim 1, wherein the total pore volume is 0.2 cm³/g or moreand the volume for pores having a pore radius of 1 nm or more is 0.2cm³/g or more.
 4. A porous titania according to claim 1, wherein theporous titania has a fibrous shape.
 5. A catalyst formed by molding theporous titania of claim
 1. 6. A catalyst comprising the porous titaniaof claim 1 and at least one catalyst component selected from the groupconsisting of V, W, Al, As, Ni, Zr, Mo, Ru, Mg, Ca, Fe, Cr and Pt.
 7. Acatalyst according claim 6, wherein the catalyst has a fibrous shape.